A novel aliphatic polyester containing a malonate group in the main chain was prepared by one-pot reaction of malonyl dichloride with ethylene glycol in the presence of triethylamine. The NMR, IR, and UV-vis studies revealed that the polymer partially underwent intra- and intermolecular Knoevenagel type self-condensation in solution and solid states, respectively, leading to formation of a certain conjugated structure in the polymer chain. The polymer exhibited a very weak, but clear, absorption around 363 nm as well as an absorption at 322 nm due to carbonyl n-pi* transition. Furthermore, the polymer exhibited blue/greenish-blue photoluminescence due to ESIPT when excited at wavelengths longer than 350 nm. This polymer is the first example of a colored and photoluminescent aliphatic polyester.